Hibernate and Standby are two different sleep options available in Windows XP.

Hibernate restore an image of your desktop, as well as all open windows and files and after that turn off your PC. When you turn your PC on again, your windows and files are open just as you left them.

Standby is a more traditional sleep mode, as it decreases the power your PC uses to almost nothing. When you choose Standby, the power to your screen, hard drive, and peripheral devices is cut.